1. Field of the Invention
This invention relates to an electrophotographic recording apparatus. More particularly, the present invention relates to an apparatus for effecting electrophotographic recording by using an electrophotographic photosensitive member, including a transparent conductor layer formed on a transparent substrate and a photosensitive layer formed on the transparent conductor layer, and by effecting exposure from the back of the photosensitive member.
2. Description of the Related Art
Existing copying machines and high-speed, high-quality printers generally use an electrophotographic recording system. This system employs a so-called "Carlson process" which uses a photosensitive member as a recording medium and effects recording through seven steps of uniform charging, image exposure, development, transfer, fixation, charge elimination and cleaning. In the charging step, a positive or negative uniform charge is applied to a surface of a photosensitive member having photoelectric conductivity and in the subsequent exposure process, a laser beam, etc., is shone onto the surface so as to eliminate a surface charge at a specific portion, thereby forming an electrostatic latent image, corresponding to the image information, on the photosensitive member. Next, this latent image is electrostatically developed to form a visible image, using a toner, on the photosensitive member. Finally, this toner image is electrostatically transferred to recording paper, and is fused by heat, light, pressure, etc., to obtain a printed matter. In the conventional recording apparatuses using this Carlson process, however, the means used for each process step are disposed around the photosensitive member. Therefore, when the size of the apparatus is reduced, these means are disposed more closely to one another around the photosensitive member. Accordingly, there is a limit to the reduction of the size of the recording system, and problems occur, that the developer scatters from the developing machine, contaminates the optical system used for image exposure means, and exerts adverse influences on printing.
In view of the problems described above, a proposal has been made to dispose an image exposure source inside the photosensitive member used in the image exposure process, and to effect light irradiation from the back of the photosensitive member (e.g. Japanese Unexamined Patent Publication (Kokai) No. 63-174072, etc.). When the image exposure source is disposed inside the photosensitive member, it becomes possible to reduce the size of the apparatus and to eliminate contamination of the optical system by the scattered developer. An LED array optical system, a laser optical system, and EL optical system, a liquid crystal shutter optical system, and so forth, can be used as the image exposure means. In order to accomplish the apparatus described above, a photosensitive member for back exposure, which has the same printing characteristics as a member which can be exposed from the outside as has been used in the prior art apparatuses, becomes necessary. The photosensitive member is normally produced by sequentially laminating conductor layers connected to the ground and photosensitive layers on a support, but the photosensitive member for back exposure must be able to transmit the rays of light irradiated from the back thereof to the photosensitive layers. To satisfy this requirement, a photosensitive member is necessary in which transparent conductor layers are laminated onto a transparent substrate.
A film having high transparency and high electrical conductivity, formed by vacuum deposition or sputtering of tin oxide (SnO.sub.2) or indium tin oxide (ITO), has been known as a conventional transparent conductor layer. However, this method requires a film formation time of as long as some dozens of minutes to one hour to form a film having a thickness of 100.ANG. on the substrate. Furthermore, excessive time and complicated production steps are necessary because the substrate must be put into and pulled out from a vacuum system. For these reasons, this method is not suitable for mass-production.